LEDs have been utilized in many monochrome lighting applications, and various manufacturers are now co-packaging triads of red, blue and green LEDs for applications where color control is desired. With such an LED triad, the hue of the emitted light is changed by varying the proportion of drive current among the red, green and blue LEDs, and the intensity of the emitted light is changed by varying the overall drive current while maintaining the proportionality of the individual red, green and blue drive currents.
While color control is often deemed to be desirable, the cost of introducing color controllable LEDs in traditionally monochrome applications can be cost prohibitive due to the increase in the number of wires required to address the individual LED devices. Instead of the traditional two wires needed for a monochrome lamp (incandescent or LED), four wires are ordinarily needed for an LED triad. This can be a particular disincentive in applications that require many lighting locations, such as in automotive interior lighting. Accordingly, what is needed is a drive system that reduces the wiring complexity required to control LED triads so that color controllable LEDs can be used more cost-effectively in a variety of applications.